What is the surface area of the triangular prism? A triangular prism. The rectangular sides are 5 feet by 4 feet, 5 feet by 5 feet, and 5 feet by 3 feet. The triangular sides have a base of 4 feet and height of 3 feet. [Not drawn to scale] 60 square feet 72 square feet 82 square feet 84 square feet